https://github.com/matthias-springer created https://github.com/llvm/llvm-project/pull/174978
Document that implementing the `RegionBranchTerminatorOpInterface` is mandatory. Omitting this interface on a block terminator that models region branching may lead to invalid/incomplete analyses and transformations. This commit does not change the op/interface semantics. It just puts in writing an assumption that is made throughout the code base. For example: - It is baked into the API design of the `RegionBranchOpInterface`. You cannot query the region successors of block terminators that do not implement the `RegionBranchTerminatorOpInterface`: `RegionBranchOpInterface::getSuccessors()` takes a `RegionBranchPoint` parameter, and such region branch points can be constructed only from `RegionBranchTerminatorOpInterface` and not arbitrary `Operation *`. - Helper functions + default interface method implementations enumerate region branch points by looking for `RegionBranchTerminatorOpInterface` and ignoring other operations. E.g., `RegionBranchOpInterface::getAllRegionBranchPoints`, default implementation of `RegionBranchOpInterface::getSuccessorRegions(Region &)`, default implementation of `RegionBranchOpInterface::getPredecessorValues`. - Core analyses such as `DeadCodeAnalysis` look for `RegionBranchTerminatorOpInterface` and misbehave when the interface is not implemented. The analysis does not (and cannot) query region successors of a region branching terminator that does not implement the `RegionBranchTerminatorOpInterface`. In practice, this means that forgetting to implement the `RegionBranchTerminatorOpInterface` may incorrectly classify regions as dead. - Other analyses / transformations that look for and depend on the implementation of `RegionBranchTerminatorOpInterface`: `mlir::getControlFlowPredecessors`, `AbstractDenseBackwardDataFlowAnalysis`, ownership-based buffer deallocation pass. >From ff3af1d7cf29ba23b04721a471175f884c5f3fa9 Mon Sep 17 00:00:00 2001 From: Matthias Springer <[email protected]> Date: Thu, 8 Jan 2026 12:58:02 +0000 Subject: [PATCH] [mlir][Interfaces] Document that `RegionBranchTerminatorOpInterface` is mandatory --- .../mlir/Interfaces/ControlFlowInterfaces.td | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/mlir/include/mlir/Interfaces/ControlFlowInterfaces.td b/mlir/include/mlir/Interfaces/ControlFlowInterfaces.td index ff99e220c179f..74c7841d52b3f 100644 --- a/mlir/include/mlir/Interfaces/ControlFlowInterfaces.td +++ b/mlir/include/mlir/Interfaces/ControlFlowInterfaces.td @@ -127,7 +127,8 @@ def RegionBranchOpInterface : OpInterface<"RegionBranchOpInterface"> { A "region branch point" indicates a point from which a branch originates. It can indicate: - 1. A terminator in any of the immediately nested region of this op. + 1. A `RegionBranchTerminatorOpInterface` terminator in any of the + immediately nested region of this op. 2. `RegionBranchPoint::parent()`: the branch originates from outside of the op, i.e., when first executing this op. @@ -147,6 +148,15 @@ def RegionBranchOpInterface : OpInterface<"RegionBranchOpInterface"> { results must have the same type. `areTypesCompatible` can be implemented to allow non-equal types. + Note: This interface works in conjunction with + `RegionBranchTerminatorOpInterface`. All immediately nested block + terminators that model branching between regions must implement the + `RegionBranchTerminatorOpInterface`. Otherwise, analyses/transformations + may miss control flow edges and produce incorrect results. Not every block + terminator is necessarily a region branch terminator: e.g., in the presence + of unstructured control flow, a block terminator could indicate a branch to + a different block within the same region. + Example: ``` @@ -379,7 +389,8 @@ def RegionBranchTerminatorOpInterface : let description = [{ This interface provides information for branching terminator operations in the presence of a parent `RegionBranchOpInterface` implementation. It - specifies which operands are passed to which region successor. + acts as a marker for valid region branch points and specifies which + operands are passed to which region successor. }]; let cppNamespace = "::mlir"; _______________________________________________ llvm-branch-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
